42 GEOLOGICAL HISTORY. [CH. 



rocks which have yielded a comparatively small number of 

 Carboniferous fossils. To this succession of limestones, shales 

 and grits the term Culm-Measures was applied by Sedgwick 

 and Murchison in 1837. The rocks of this series occupy a 

 trough between the Devonian rocks of North and South 

 Devon. While some authorities have correlated the Culm- 

 Measures with the Millstone Grit, others regard them as repre- 

 senting a portion of the true Coal-Measures, as well as the 

 Carboniferous and Lower Limestone Shale\ It has recently 

 been shown that among the lower Culm strata there occur 

 bands of ancient deep-sea sediments, consisting of beds of 

 chert containing siliceous casts of various species of Radiolaria. 

 There can be no doubt that the discovery of deep-sea fossils 

 in this particular development of the British Carboniferous 

 system leads to the conclusion that "while the massive 

 deposits of the Carboniferous limestone — formed of the skele- 

 tons of calcareous organisms — were in process of growth in 

 the seas to the North, there existed to the South-west a 

 deeper ocean in which siliceous organisms predominated and 

 formed these siliceous radiolarian rocks ^." 



The Upper Culm-Measures consist of conglomerates, grits, 

 sandstones and shales with some plant remains and other 

 fossils, and constitute a typical set of shallow water sediments. 

 In Westphalia, the Harz region, Thuringia, Silesia and Moravia 

 there are rocks corresponding to the Culm-Measures of Devon, 

 and some of these have also afforded evidence of deep water 

 conditions. 



S. W. England, 8. Wales, Derbyshire and Yorkshire, In 

 these districts the Carboniferous limestone reaches a con- 

 siderable thickness ; in the Mendips it has a thickness of 

 8000 feet, and in the Pennine chain of 4000 feet. At the base 

 of this limestone series there occurs in the southern districts 

 the so-called loAver limestone shale, consisting of clays, shales 

 and sandy beds. Above the limestone we have the Millstone 

 gxit and Coal-Measures ; but in the Pennine district there is 

 a series of rocks consisting of impure limestones and shales, 



1 Woodward, H. B. (87), p. 197. 



2 Hinde and Fox (95), p. 662 



